Dimming circuit and apparatus for gaseous discharge lamps



L. L. GENUlT June 13, 1961 DIMMING CIRCUIT AND APPARATUS FOR GASEOUSDISCHARGE LAMPS 2 Sheets-Sheet Filed Sept. 2, 1959 w n. H r m I Z t Z 2Sheets-Sheet L. L. GENUIT w w; a n 4 r m w 6 4 M m f w a. w E m W m m my m m 5 f m M wm a ww M 4 U M Wm m i I! L NJ A M W W 7 6 b I w a w a m Ik m m z F s M A D 0 MM 0 5 .ll .Mmvx w\ \k\w w\b ZNnfi A N85 NW3? a Q. Qm v a w l u M 7 F 0 0 5 June 13, 1961 DIMMING CIRCUIT AND APPARATUS FORGASEOUS DISCHARGE LAMPS Filed Sept. 2, 1959 ilnited States Patent2,988,670 DIMMING CIRCUIT AND APPARATUS FOR GASEOUS DISCHARGE LAMPSLuther L. Genuit, Danville, Ill., assignor to General Electric Company,a corporation of New York Filed Sept. 2, 1959, Ser. No. 837,624 Claims.(Cl. 315-98) This invention relates to an electrical circuit andapparatus for regulating the luminous intensity of gaseous dischargelamps and more particularly to a dimming circuit and apparatus foroperating at various levels of luminous intensity one or morefluorescent lamps from an alternating current source.

The invention is primarily intended for use in connection with gaseousdischarge lamps having activated filamentary cathodes which are heatedduring the operation of the lamp by a constant supply of current. Sincethe cathodes are continuously heated in this manner, the cathodes can bebrought to thermionic emission at voltages below the ionization voltageof the gas or vapor in the lamp. This characteristic makes it possibleto operate such lamps at various levels of intensity. Commercially,lamps having heated cathodes are referred to as rapid start or hotcathode lamps.

Apparatus presently in commercial use for operating hot cathode lamps atvarious levels of luminous intensity are generally provided with somemeans for introducing a voltage spike into the lamp circuit for firingthe lamp, particularly at the lower levels of luminous intensity. In acopending application filed in the name of Charles E. Strecker on thesame date as this application and assigned to the assignee of thepresent application, a dimming circuit and apparatus is disclosedemploying a peaking means to impress a voltage spike on the lampcircuit. This invention is concerned with an improvement of theapparatus and circuit disclosed in the aforementioned copendingapplication.

Although the foregoing apparatus and circuit satisfactorily operates arapid start lamp at a wide range of luminous intensity levels, it wasfound that a flutter or jump in light output occurs at a point in thelow intensity region as the dimming control is advanced from the dimposition to the bright position. This invention involves an improvementwhich eliminates the flutter in the light output and is applicable tothe foregoing apparatus and circuit and generally to dimming controlsystems employing a peaking means to impress voltage spikes in a heatedcathode lamp circuit.

Accordingly, a general object of the invention is to provide a new andimproved circuit and apparatus for adjusting the luminous output ofelectric discharge lamps.

A specific object of the invention is to eliminate the flutter in thelight output of a hot cathode lamp operated at varying levels ofluminous intensity in dimming control circuits employing a means toimpress a voltage spike in the lamp circuit.

Another object of the invention is to provide a peaking circuit havingimproved noise and structural characteristics.

Still, another object of the invention is to provide an improved peakingcircuit, the components of which can be so arranged in a case with othercomponents of the dimming control system along a longitudinal axis sothat the transverse dimensions of the case are at a minimum to permitthe case housing the components to be efiectively concealed in alighting fixture.

In accordance with the invention, a nonlinear reactor is included inseries circuit relationship with the output terminals of an inductivedevice generating a voltage spike and the high leakage reactancesecondary of a ballast transformer in a dimming control system. It wasfound 'ice that the introduction of this nonlinear reactor in effectlimits the lamp current when the luminous intensity is at the criticallow levels where fluttering of luminous intensity may occur. Thus, thenonlinear reactor eliminates such fluttering in the region of lowintensity levels. Further, it was found that the addition of thenonlinear reactor into the circuit in accord with the invention does notappreciably reduce the lamp current when the lamp is being operated athigher levels of luminous intensity. This condition is brought aboutbecause of the saturating characteristic of the reactor.

A dimming control, as referred to herein, is an apparatus, such as avariable transformer, which is used to vary the input voltage suppliedto the lamp terminals and is usually at some remote location from thelighting fixture. The dimming control is used in conjunction with adimming control system, which as a matter of commercial practice, ishoused in a separate case and is generally located in or near the lightfixture. A nonlinear transformer, as the term is used herein, is aninductive device and includes such devices as saturable reactors,transformers and autotransformers having saturating characteristicswhich for practical purposes are effective in the circuit only duringthe period their cores saturate and desaturate. A voltage spike isdefined as a sharp voltage increment or impulse, in contradistinction topeak voltage, which is the maximum net open circuit voltage across thelamp and includes the voltage spike when the spike is superimposed onthe lamp circuit.

The subject matter which I regard as my invention is set forth in theappended claims. The invention itself, however, together with furtherobjects and advantages thereof may be understood by referring to thefollowing description taken in connection with the accompanying drawingsin which:

FIG. 1 is a schematic circuit diagram of a dimming control system inwhich the invention is embodied:

FIG. 2. illustrates two curves showing light intensity plotted againstdimming control output, the letter A identifying the curve obtained whenthe nonlinear reactor of the invention is shorted out in the circuitshovm in FIG. 1 and the letter B identifying the curve ob tained withthe nonlinear reactor of the invention in the circuit as shown in FIG.1;

FIG. 3 illustrates the curvm for the peak open circuit and the root meansquare open circuit voltages at the lamp plotted against the dimmingcontrol output for the circuit shown in FIG. 1;

FIG. 4 shows the noise level versus dimming control output curves for acold and hot condition of operation of the circuit shown in FIG. 1, thedashed line curve representing a hot condition of operation for acomparable circuit of the prior art;

FIG. 5 is a plan view of the dimming control system case with the coverplate removed to show the longitudinal arrangement of the componentparts of the system;

FIG. 6 is a sectional view along line 6-6 of FIG. 5; and,

FIG. 7 is a diagrammatic illustration of the core and windingarrangement of the peaking circuit of the invention.

The rectangle formed by the dashed lines of FIG. 1 encloses the dimmingcontrol system of the invention. The illustrated dimming control systemstarts and maintains the luminous intensity of an electric dischargelamp 10 which is shown as a fluorescent lamp. In the illustratedcircuit, the lamp 10 may be a 40-watt rapid start fluorescent lamp whichcomprises an elongated tubular cylindrical envelope 11 having sealedinto the ends thereof the filamentary cathods 12 and 13, which areillustrated in the form of a coil of tungsten wire. The fila ments 12,13 are activated with oxides of alkaline earth metals, such as mixturesof barium and strontium oxides. The envelope is filled with a startinggas, such as argon, at a pressure of a few millimeters and a smallquantity of mercury. The interior of the envelope 11 is coated with aphosphor which converts the ultraviolet radiation produced by thedischarge into visible light. The outside surface of the envelope 11 iscoated with a water-repellent substance which makes it possible to startthe lamp 10 under normal atmospheric conditions and low voltages whenthe lamp 10 is positioned close to a conducting means and a suitablepotential diiference is provided with respect to one of the cathodes 12,13. The conducting plate 14 located in proximity to the lamp envelope 11serves as such a conducting means and is connected to ground. In acommercial fixture, the metal reflector of the grounded fixture mayperform the function of the conductive plate 14. The normal spacing ofthe plate 14 is approximately three-eighths /s) of an inch from theenvelope 11.

The reference character 15 designates generally the ballastauto-transformer which includes a primary 16, a high leakage reactancesecondary 17, a second secondary 18, and the two cathode heatingwindings 19 and 20.

As shown in FIGS. and 6, the magnetic core 21 of the ballastautotransformer 15 is comprised of a laminated central winding leg 22and the E-shaped laminations 23 which abut the sides of the winding leg22. The middle legs of the E-shaped laminations 23 form magnetic shunts24, 25, the ends of which are spaced from the central winding leg 22 byan air gap 27.

The coil structure 28 includes the primary winding 16, the cathodeheating windings 19, 20, and the second secondary 18. These windings aredisposed about the central winding leg 22 in window 29. The secondaryhigh leakage reactance winding 17 of the autotransformer 15 is disposedabout the central winding leg 22 in window 30.

Referring again to FIG. 1, the cathode heating windings 19, 20- aretightly coupled with the primary 16 in order that the supply of cathodeheating current is maintained at a constant value. The loose couplingbetween the primary 16 and secondary winding 17 is required in order toobtain the high leakage reactance which is necessary to limit thecurrent flowing through the lamp which has a negative resistancecharacteristic.

The second secondary winding 18 is connected in series with the powerfactor capacitor 31 across the power supply by terminal connections 32,33. The purpose of the second secondary Winding 18 is to increase thevoltage across the capacitor 31 above the source voltage, therebyreducing the size of the capacitor required to correct the over-allpower factor of the circuit. The capacitor 3 1 draws a leading currentfrom the primary 16 which offsets the lagging magnetizing current.

It should be readily apparent that by the elimination of the capacitor31 and the second secondary winding 18 that the circuit can be readilyconverted to a low power factor ballast arrangement. As will behereinafter more fully described, such a ballast arrangement may be usedwith each lamp when more than one lamp is to be operated by a singlepeaking circuit in accordance with the invention.

The cathode heating windings 13, 20 are connected across the cathodes12, 13 by means of conductors 34, 35 and 36, 37 respectively. Thecathode heating winding 20 is shown in an autotransformer relationshipwith the primary 16, while the other cathode heating winding 19 is shownin an isolated secondary relationship with the primary 16. It should beevident that a circuit designer has a considerable amount of flexibilityin locating the cathode heating windings, providing the windings willsupply a constant heating current to the cathodes 12, 13.

The primary winding 16 is connected across a normal 120 volt, 60 cyclecommercial power supply which is connected with the circuit at theterminals 38, 39, the terminal 38 being the high side and the terminal39 being the low side of the supply. The low side is arranged so that itis at the same voltage potential as inductive plate 14 and is groundedthrough a resistor 26 to the ground 40, as shown.

One end of the high leakage reactance secondary 17 is connected by meansof a conductor 70 to a nonlinear reactor 71. The nonlinear reactor 71 isalso connected by means of a conductor 42 to a secondary winding 43 of anonlinear transformer 44, which has a primary winding 45. Thus, thesecondary winding 17 of the ballast transformer 15, the nonlinearreactor 71, and the secondary winding 43 are connected in series circuitrelationship.

The primary 45 and secondary winding 43, as shown in FIG. 1, are inautotransformer relationship. A tap 46 of the nonlinear transformer 44is connected with one end of a linear reactor 47, while the other end ofthe linear reactor 47 is connected to the high voltage side of the powersupply at connection 48.

The primary winding 45 of the nonlinear transformer 44 is connected to aslider or variable tap 49 of a variable autotransformer or dimmingcontrol 56 connected across the power supply. In the practice of theinvention, a stepdown or a step-up variable autotransformer may be usedas required. In one commercial exemplification of the invention avariable autotransformer having a range from 0 to 130 volts alternatingcurrent was employed. In such an arrangement, a slight step-up involtage is obtained when volt power supply is used.

The peaking circuit includes the nonlinear reactor 71, the linearreactor 47 and the nonlinear transformer 44, having the primary 45 andthe secondary 43, as shown in FIG. 1, connected in autotransformerrelationship. This permits the dimming control system to make maximumuse of the voltage of the device.

In a dimming control system operating a 40-watt rapid start lamp, it isdesirable that an open circuit peak voltage of approximately 325 voltsbe maintained at the lamp terminals over the widest range of dimmingcontrol settings. An advantage of the peaking circuit of the inventionis that the voltage spike supplied by the secondary 43 of the nonlineartransformer 44 will progressively decrease as the setting of the dimmingcontrol is adjusted to increase the input voltage to the lamp 10 withouta flutter in luminous intensity output.

In FIG. 7, a more detailed schematic illustration of the core structureand winding arrangement of the components of the peaking circuit of theinvention is shown. The peaking circuit is comprised of the nonlinearreactor 71, the nonlinear transformer 44 and the linear reactor 47connected as shown. The nonlinear reactor 71 includes a winding 72 and amagnetic core structure 73. The nonlinear transformer 44 includes theprimary winding 45, the secondary winding 43, a tap 46, and a magneticcore structure 53. The linear reactor 47 includes a winding 51 and amagnetic core structure 52.

One end of the winding 51 of the linear reactor 47 is connected by meansof a conductor 54 to the tap 46. The other end has a terminal 48 forconnection to the high side of the power supply. A terminal 56 of theprimary winding 45 provides a means for connecting to the adjustable tap49 of the dimming control 50. A conductor 55 connects the secondarywinding 43 of the nonlinear transformer 44 with the winding 72 of thenonlinear reactor 71, the windings 43 and 72 being in series circuitrealtionship. The terminal 74 of the winding 72 provides a means forconnecting the nonlinear reactor 71 in series circuit relationship withthe high leakage reactance secondary 17.

The magnetic core structure 53 is built of a sufficient number oflaminations to provide a relatively small crosssectional area that makesthe core readily saturable. In the illustrated exemplification of theinvention, eight U shaped laminations are used, adjacent laminationsbeing reversed to break the joints and being constructed of thinsections of grain oriented electrical steel.

The mangetic core structure 52 of the linear reactor 47 is built up oftwo adjacent stacks of E-shaped laminations 57 with the ends of theirlegs in an abutting relationship. The winding 51 is Wound around amiddle leg 58 formed by the juncture of the central legs of thelaminations 57.

In building up the magnetic core structure 73 of the nonlinear reactor71, small groupings of thin E-shaped laminations are stacked in analternately staggered and inverted relationship. In the exemplificationof the invention four laminations are used per grouping and a total ofseven groupings are inverted and staggered as shown.

How the voltage spike is superimposed on the open circuit voltage acrossthe lamp terminals will now be described. The total flux between thelinear reactor 47 and the nonlinear transformer 44 is distributedbetween their respective cores 52, 53. The variation of total flux issubstantially sinusoidal and cycles at the frequency of the powersupply. At the beginning of a cycle, saturation occurs very quickly inthe legs of the core 53 of the nonlinear transformer 44. The flux in theliear reactor 47, however, increases slowly until the flux in thenonlinear transformer 44 passes the point of saturation at which timethe flux in the linear reactor 47 undergoes a rapid increase. Since theflux in the core 53 of the nonlinear transformer 44 undergoes a veryrapid change at the beginning of each half cycle, a voltage spike isgenerated in its secondary winding 43. Since this voltage spike occursapproximately at the same time that the input lamp voltage from thedimming control 50 and ballast secondary 17 is at its maximum value andsince the spike generated and the input lamp voltage are of the samepolarity, the spike is superimposed on the sinusoidal input lampvoltage.

In view of the fact that the voltage across the primary winding 45 ofthe nonlinear transformer 44 increases as the slider 49 of the dimmingcontrol is moved away from a position of maximum brightness B, the spikegenerated in the secondary 43 will increase to maintain a fairlyconstant open circuit peak voltage at the lamp 10. Thus, it is possiblefor the dimming control system to reliably operate the lamp at a widerange of luminous intensity levels.

Referring now to FIGS. 5 and 6, the arrangement of the principalcomponents in the dimming control system case 41 is shown. The powerfactor correcting capacitor 31 is located at one end of the case 41 andis separated from the ballast transformer by an insulator 63. Ashereinbefore described, the core structure 21 is formed by the E-shapedlaminations butting against the laminations of the central leg 22. Thecoil structures 28 and 17 may be held against the central leg 22 bywedges (not shown).

In an adjacent portion of the case 41 and separated from the ballasttransformer 15 by an insulator 65 is the nonlinear reactor 71. Thewinding 72 is held securely against the central winding leg 61 by awedge 62.

The nonlinear reactor 71 is separated from the nonlinear transformer 44by the insulator 59. The coil structure 66, which includes the primaryWinding 45 and secondary Winding 43 is disposed around a leg 67 of thecore structure 53 formed by alternately inverted U-shaped laminations. AU-shaped positioner 74 serves to firmly hold the coil 66 in a givenlocation in the case 41.

Separated from the nonlinear transformer 44 by an insulator 6!) is thelinear reactor 47. The winding 51 is disposed about the middle leg 58 bytwo adjacent stacks of E-shaped laminations 57 as hereinbeforedescribed. The linear reactor 47, as well as the other components of thedimming control system, are embedded in a suitable potting compound,such as asphalt.

It is to be noted that none of the laminations employ any unusualconfigurations or have any narrow legs or bridged section. Thelaminations of the ballast transformer 15 are of the type commerciallyused for normal operation of fluorescent lamps. The core structures 21,

52, 53 and 73 are separate units. Thus, the dimming control system ofthis invention provides for the magnetic isolation, so far as ispractically feasible, of all of the peaking and ballast elements of thesystem. It was found that such an arrangement results in an appreciablereduction in noise as compared to other dimming control systems of theelectromagnetic type. The noise level versus dimming control outputcurves of FIG. 4 for the cold and hot condition of operation of thedimming control system of the invention indicate that the noise leveldoes not appreciably rise over the entire dimming control output range.The dashed line curve is representative of the noise characteristic of acomparable electromagnetic dimming control system of the prior art.Therefore, the dimming con-trol system of this invention is particularlysuitable for many applications, such as, stage, auditorium, residentialand funeral parlor lighting purposes where a low noise level ispreferable.

The operation of the dimming control system of FIG. 1 will now bedescribed in more detail. When the slider 49 of the dimming control 50is at position B, the open circuit voltage across the primary andsecondary voltages of the ballast transformer 15 are sufiicient to firethe fluorescent lamp 10. Once the lamp 10 ignites, the high leakagereactance of the secondary winding 17 of the ballast transformer 15provides the necessary ballasting action required because of thenegative resistance characteristic of the lamp 10. The cathode heatingwindings 19, 20 are closely coupled to the primary winding 16 of theballast transformer 15 and provide the filaments 12, 13 respectivelywith a substantially constant current for heating the cathodes of thelamp 10.

It is to be noted, that when the slider 49 is in the position B, novoltage appears across the primary 45 of the nonlinear transformer 44and the reactor 47 and no voltage spike is introduced by the secondary43 into the lamp circuit. In efiect, the primary 45 and the reactor 47are by-passed and the lamp 10 operates in the normal manner.

As the slider 49 is moved away from the position of maximum brightnessB, a progressively increasing voltage is being applied to the primary 45of the nonlinear transformer 44 and the linear reactor 47. Also, as theslider 49 is moved in this direction, the sinusoidal input voltage tothe lamp 10 and the current being supplied to the lamp 10correspondingly diminish. With a diminishing current supply to the lamp10, the energy emitted at the cathodes decreases and the fluorescentcoating of the lamp receives a reduced amount of radiation with theresult that the luminous intensity of the lamp declines.

Unless some means is provided in the dimming control system for firingthe lamp 10, it would normally stop discharging when the input voltagereaches a certain level. The peaking circuit provides the necessaryvoltage spike at each half cycle to refire the lamp. Since the voltagespike occurs at the frequency of 60 cycles per second, the operation ofthe lamp 10 is in effect continuous.

It is to be noted that as a decreasing input voltage appears across thelamp 10 to cause dimming, an increasing voltage is being applied acrossthe primary 45 of the nonlinear transformer 44 and the linear reactor 47to proportionately step up the voltage spike. Such an arrangementprovides a substantially constant open circuit peak voltage for a widerange of the dimming control settings, and results in stable lampoperation at the selected levels of luminous intensity.

The stability of operation inherent in the dimming control system of theinvention is evidenced by the open circuit voltage curves of FIG. 3. Itis to be noted that open circuit peak voltage at the lamp terminals issubstantially uniform over the entire range of dimmer control settings.

The nonlinear reactor 71 in series circuit relationship with thesecondary 43 of the nonlinear transformer 44 serves the purpose ofeliminating a fluttering in the luminous intensity of the lamp which mayoccur. This fiutter is illustrated by the sharp rise in curve A of FIG.2.. Such fluttering may occur at a point in the region of low powerinput to the lamp. The nonlinear reactor 71 functions to limit the lampcurrent when the power input is at critical low levels. As shown by thecurve B of FIG. 2, the introduction of the nonlinear reactor 71 does nothave an appreciable effect on the intensity levels but has the effect ofsmoothing out the curve. This is due to the fact that the lamp currentis not appreciably reduced when the lamp is operated at the higherlevels of luminous intensity because of the saturating characteristic ofthe reactor 71.

From the foregoing description, it should be apparent that a singlepeaking circuit of the invention and a single dimming control can beused to operate a plurality of lamps as well as a single lamp. In theembodiment illustrated in FIG. 1, a second secondary 18 is used inconjunction with the power factor correcting capacitor 31 for thepurpose of reducing the size of the capacitor. As is well-known in theart, the power factor can be. corrected by other methods withoutcoupling the winding 18 with a ballast transformer.

While I have described above a particular embodiment of the invention,many modifications may be made. It is to be understood, therefore, thatI intend by the ap pended claims to cover all such modifications as fallwithin the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. Apparatus for operating a hot cathode fluorescent lamp at variouslight intensity levels regulated by a dimming control energized by analternating current supply and having an adjustable tap, said apparatuscomprising a ballast means having a primary energized by saidalternating current supply and a high leakage reactance secondary, apeaking means including a linear reactor and a first nonlinear inductivedevice connected in series for producing a voltage spike in saidnonlinear device variable in magnitude as the dimming control isregulated, a second nonlinear inductive device for eliminating flutterin light intensity at low dimming control settings, circuit means forapplying a voltage across said serially connected linear reactor andfirst nonlinear inductive device, said first nonlinear device having apair of output terminals for applying said voltage spike to said lampand circuit means connecting said output terminals, said secondnonlinear inductive device, said high leakage reactance secondary andsaid lamp in series circuit relationship with said adjustable tap.

2. Apparatus for operating a hot cathode fluorescent lamp at variouslight intensity levels regulated by a dimming control energized by analternating current supply including a high and a low side and having anadjustable tap, said apparatus comprising a ballast means having aprimary energized by said alternating current supply and a high leakagereactance secondary, a peaking means in cluding a linear reactor and anonlinear transformer having a primary and a secondary, a nonlinearreactor for eliminating flutter in light intensity at low dimmingcontrol settings, circuit means for connecting said adjustable tap, saidprimary of the nonlinear transformer, said linear reactor and the highside of the alternating current supply in series circuit relationshipand circuit means for connecting said secondary of said nonlineartransformer, said nonlinear reactor, said high leakage reactancesecondary, said lamp and said low side of said alternating currentsupply in series circuit relationship.

3. A peaking circuit for superimposing a voltage spike on an inputvoltage supplied to a hot cathode fluorescent lamp from an alternatingcurrent source and regulated by a dimming control having an adjustabletap, said lamp being connected across a ballast transformer having aprimary and a high leakage reactance secondary, said 8 peaking circuitcomprising a nonlinear transformer including a primary, a secondary anda tap between said secondary and primary; said primary having a terminalfor connecting with said adjustable tap; a nonlinear reactor connectedin series with said secondary of the nonlinear transformer and having aterminal for connecting said serially connected nonlinear reactor andsaid secondary in series circuit relationship with said high leakagereactance secondary; and a linear reactor connected to said tap of thenonlinear transformer and having a terminal for connecting to saidalternating current source.

4. A dimming control system for operating a hot cathode fluorescent lampat various light intensity levels regulated by a dimming controlenergized by an alternating power supply including a low and a high sideand having an adjustable tap, said system comprising a high leakagereactance transformer having a primary connected across said powersource and a high leakage reactance secondary; a linear reactor; anonlinear transformer having a primary and secondary, said linearreactor and said primary of the nonlinear transformer being connected inseries across said adjustable tap and said high side of the powersource; a nonlinear reactor for eliminating flutter in the lightintensity for low dimming control settings; and circuit means forconnecting said secondary of the nonlinear transformer, said nonlinearreactor, said high leakage reactance secondary, said lamp and said lowside of the power source in series circuit relationship.

5. A peaking circuit for superimposing a voltage spike on an inputvoltage supplied to a hot cathode fluorescent lamp from an alternatingcurrent source and regulated by a dimming control having an adjustabletap, said lamp being connected across a ballast transformer having aprimary and a high leakage reactance secondary, said peaking circuitcomprising a nonlinear transformer having a core structure formed ofalternately inverted U- shaped laminations including a primary and asecondary winding disposed on said core structure in autotransformerrelationship and a tap disposed between primary and secondary windings,said primary having a terminal for connecting with said adjustable tap;a nonlinear reactor being connected in series with said secondarywinding and having a terminal for connecting said secondary winding withsaid high leakage reactance in series circuit relationship; and a linearreactor connected to said tap of the nonlinear transformer and having aterminal for connecting to said alternating current source.

6. A peaking circuit for superimposing a voltage spike on an inputvoltage supplied to a hot cathode fluorescent lamp from an alternatingcurrent source and regulated by a dimming control having an adjustabletap, said lamp being connected across a ballast transformer having aprimary and a high leakage reactance secondary, said peaking circuitcomprising a nonlinear transformer including a primary, a secondary andtap between said secondary and primary, said primary having a terminalfor connecting with said adjustable tap; a nonlinear reactor having acore structure formed of alternately inverted and staggered groupings ofE-shaped laminations and a winding disposed on said core structure, saidnonlinear reactor being connected in series with said sec ondary of thenonlinear transformer and having a terminal for connecting said seriallyconnected nonlinear reactor and said secondary in series circuitrelationship with said high leakage reactance secondary; and a lineareluding a high side and a low side and having an adjustabl'e tap, saidapparatus comprising a ballast means having a primary energized by saidalternating voltage supply and having a high leakage reactancesecondary; a peaking means including a linear reactor, a nonlinearreactor and a nonlinear transformer having a primary and a secondary;circuit means for connecting said primary of said nonlinear transformerand said linear reactor in series circuit relationship between saidadjustable tap and said high side of the alternating voltage supply; andcircuit means connecting said secondary of the nonlinear transformer,said nonlinear reactor, said high leakage reactance secondary, said lampand said low side of the alternating voltage supply in series circuitrelationship.

8. Apparatus for operating a hot cathode fluorescent lamp at variousbrightness levels regulated by a dimming control energized by analternating current supply including a high and a low side and having anadjustable tap, said apparatus comprising a ballast autotransformerhaving a primary energized by said alternating current supply and havinga high leakage reactance secondary; a linear reactor; a nonlinearreactor; a nonlinear transformer having a primary, a secondary inautotransformer relationship with said primary and a tap between saidprimary and secondary; circuit means connecting said secondary of thenonlinear transformer, said nonlinear reactor, said high leakagereactance secondary, said lamp and said low side of the alternatingcurrent supply in series circuit relationship; and circuit meansconnecting said adjustable tap, said primary of the nonlineartransformer and said linear reactor and said high side of thealternating current supply in series circuit relationship, said ballastautotransformer, said linear reactor, said nonlinear reactor, and saidnonlinear transformer being magnetically isolated from each other.

9. Apparatus for operating a hot cathode fluorescent lamp at variouslight intensity levels regulated by a dimming control energized by analternating current supply, said apparatus comprising a ballast meansfor limiting the current supplied to said lamp and having a pair ofterminals, a nonlinear reactor for eliminating flutter in lightintensity at low dimming control settings, a peaking means for providingsaid lamp with a voltage spike to aid in firing said lamp and having apair of output terminals, and circuit means for connecting saidterminals of said ballast means, said nonlinear reactor, said outputterminals of said peaking means and said lamp in series circuitrelationship.

10. Apparatus for operating a hot cathode fluorescent lamp at variouslight intensity levels regulated by a dimming control energized by analternating current supply and having an adjustable tap, said apparatuscomprising a ballast means having a pair of current limiting terminals,a peaking means including a linear reactor and a first nonlinearinductive device connected in series for producing a voltage spike insaid nonlinear device variable in magnitude as the dimming control isregulated, a second nonlinear inductive device for eliminating flutterin light intensity at low dimming control settings, circuit means forapplying a voltage across said serial connected linear reactor and saidfirst nonlinear inductive device, said nonlinear device having a pair ofoutput terminals for applying said voltage spike to said lamp andcircuit means connecting said output terminals, said second nonlinearinductive device, said pair of current limiting terminals and said lampin series circuit relationship with said adjustable tap.

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